During cooking, most foodstuffs undergo chemical non-reversible reactions. For example, many foodstuffs release liquids and gases/aromas. Some of these aromas are unpleasant and the release of them to the surrounding air is desired process when cooking.
The purpose of pasteurizing foodstuffs is to extend the shelf life of the product, hence allowing safe and enjoyable consumption of the food many days or weeks after its preparation. Pasteurization is often achieved through a heat treatment of the product and sometimes cooking and pasteurization can be achieved in one step.
After heat treatment, the foodstuff is sensitive to manipulation and there is a risk of recontamination. To cook/pasteurize inside a pack eliminates said risk and ensures a potentially safer route to extended shelf life for the product.
To ensure that the coldest point in the package obtains a temperature of above 65° C., it has been necessary to apply so much heat that the pressure in the package has increased substantially. To avoid that such an increased pressure breaks the seal of the package, a counter-pressure has been applied outside the package. However, applying such a counter-pressure means that the boiling point of water is increased, which in turn results in that the hottest points in the package are no longer protected from overheating by flash cooling at 100° C. This causes the food to suffer organoleptically, i.e. deteriorate through non-desirable chemical irreversible reactions.
Cooking with a one-way valve is known through companies like Valvopack/Nutripack and Micvac. The benefit is that higher core temperature can be reached without the need of applying a counter-pressure and at the same time allow undesired gases/aromas to escape through the valve, hence creating a more natural taste as the process resembles what happens in a pot on the stove or in an open tray in the oven.